A multiparametric approach to a study of the penetration phase of Trypanosoma cruzi-vertebrate cell interactions is utilized in order to develop a mathematical model of the phenomenon. The effects of varying physiologic parameters are being studied in this system and compared with other host-parasite systems such as Toxoplasma gondii-vertebrate cell interactions. Low-light-level video techniques have been expanded to include studies of the mechanism of penetration of vertebrate cells by T. cruzi trypomastigotes. BIBLIOGRAPHIC REFERENCES: Dvorak, J.A., Schuette, W.H., and Whitehouse, W.C.: The application of low light level video techniques to biomedical research. Optical Engineering SPIE 78: 155-106, 1976. Dvorak, J.A. and Howe, C.L.: The effects of Lampit (Bayer 2502) on the interaction of Trypanosoma cruzi with vertebrate cells in vitro. Am. J. Trop. Med. Hyg. 26: 58-63, 1977.